1. Field of the Invention
The present invention relates to thin film graphitic systems and, more specifically, to a method of growing ultra-thin graphitic layers.
2. Description of the Prior Art
Graphene is a semimetal consisting of a single atomically thin sheet of graphite. As used here, “ultra-thin graphitic layer” includes one or more (e.g., up to 300) graphene sheets. An ultra-thin graphitic layer may be on a silicon carbide substrate. Ultra-thin graphitic layers have a potential use as charge transporting and semiconductor materials for microelectronics.
Ultra-thin graphitic layers form on silicon carbide crystal substrates when the silicon carbide substrate is heated in a vacuum to temperatures in the range of 1100° C. to 2000° C. At this temperature, silicon evaporates from the surface causing the surface to become carbon rich. Carbon on the surface is stable as an ultra-thin graphitic layer. Typically, ultra-thin graphitic layers are grown on silicon carbide crystals by heating the crystals in ultra-high vacuum at high temperatures. The growth process involved the sublimation of silicon from the silicon carbide surface so that the surface becomes carbon rich. The carbon at the surface then forms graphitic layers.
The properties of ultra-thin graphitic layers grown on silicon carbide crystals are essentially the same as those of a single graphene sheet. Ultra-thin graphitic layers on silicon carbide crystals can be patterned using existing microelectronics lithography methods to produce electronically functional structures. Consequently, as for a single graphene sheet, ultra-thin graphitic layers grown on silicon carbide crystals can be used as an electronic material.
For graphene and multilayered graphene to become semiconducting for use in electronic applications, the multilayered graphene should be patterned into ribbons that are typically narrower than about 20 nm. To produce ribbons that are this narrow, non-standard nanofabrication techniques are employed. However, many such techniques are difficult to implement for large-scale production.
The graphene sheet that is in contact with the silicon carbide substrate is called the “interface layer.” The interface layer acquires an electronic charge, whereas the other graphene layers are substantially uncharged. Due to this charge, the conductivity of the interface layer is particularly large and therefore carries most of the current when voltages are applied to multilayered graphene ribbons. While this conducting interface layer has advantages for some applications, it is disadvantageous for many electronic device structures.
Growing ultra-thin graphitic layers on silicon carbide crystals using the ultrahigh vacuum method mentioned above can be a time consuming and complex process. This is because the silicon carbide crystal has to be introduced into an ultra-high vacuum system, in which the residual gas pressures are below 10−9 Torr, which is difficult to achieve at a large scale. Also, it is difficult to elevate the temperatures of a vacuum chamber uniformly so that all of the silicon carbide crystal heats to the high temperature required for the formation of high-quality ultra-thin graphitic layers. Furthermore, the quality of the ultra-thin graphitic layers grown using an ultra-high vacuum chamber tends to be poor and the ultra-thin graphitic layers show evidence of degradation, possibly due to chemical reactions with residual background gasses. Thus, defects are common in such ultra-thin graphitic layers.
Therefore, there is a need for method of creating ultra-thin graphitic layers on a large scale.
Therefore, there is also a need for method of creating ultra-thin graphitic layers that have few defects.